function.c (struct epi_info): New field const_equiv.

function.c (struct epi_info): New field const_equiv.

	PR/6552
	* function.c (struct epi_info): New field const_equiv.
	(update_epilogue_consts): New function.
	(keep_stack_depressed): Clear new field and verify scratch register
	doesn't have it set.
	Call new function via note_stores.
	(handle_epilogue_set): Allow setting SP equiv reg in different mode.
	Allow PLUS where second operand is register known set to constant.
	(emit_equiv_load): Write load using proper mode if source different.
	* config/mips/mips.md (return_internal): Put (return) first.

From-SVN: r73609